Bijvoetite-(Y)

Bijvoetite-(Y) is a very rare rare-earth and uranium mineral[2][3] with the formula (Y,REE)8(UO2)16(CO3)16O8(OH)8·39H2O.[3][4] When compared to the original description, the formula of bijvoetite-(Y) was changed in the course of crystal structure redefinition.[1] Bijvoetite-(Y) is an example of natural salts containing both uranium and yttrium, the other examples being kamotoite-(Y) and sejkoraite-(Y).[5][6] Bijvoetite-(Y) comes from Shinkolobwe deposit in Republic of Congo, which is famous for rare uranium minerals. The other interesting rare-earth-bearing uranium mineral, associated with bijvoetite-(Y), is lepersonnite-(Gd).[2]

Bijvoetite-(Y)
General
CategoryCarbonate mineral
Formula
(repeating unit)		(Y,REE)8(UO2)16(CO3)16O8(OH)8•39H2O
Strunz classification5.EB.20 (10 ed)
5/F.06-30 (8 ed)
Dana classification16b.2.4.1
Crystal systemMonoclinic
Crystal classSpheroidal (2)
(same H-M symbol)
Space groupB21
Unit cella = 21.23, b = 12.96,
c = 44.91 [Å], β = 90.00° (approximated); Z = 4
Identification
ColorYellow
Crystal habitPlates
Cleavage{001}, good
Mohs scale hardness2
LusterVitreous
StreakLight yellow
DiaphaneityTransparent to translucent
Density3.97 (measured)
Optical propertiesBiaxal (+)
Refractive indexnα = 1.60, nβ = 1.65, nγ = 1.72 (approximated)
PleochroismColorless (X), pale yellow (Y), deep yellow (Z)
2V angle84° (measured)
Other characteristics Radioactive
References[1][2][3][4]

The mineral is named after the Dutch chemist and crystallographer Johannes Martin Bijvoet.

Notes on chemistry

Other rare-earth elements substituting for yttrium ("REE" in the given formula) are mainly neodymium, samarium, gadolinium, and dysprosium, with minor cerium, europium, terbium and erbium.[1] This is in slight opposition to the original reported analysis, that had dysprosium, gadolinium and terbium as main substituting REE.[3]

Occurrence and association

Bijvoetite-(Y) was found in the Shinkolobwe dolomite-hosted uranium deposit, Republic of Congo, where it occurs in an oxidation zone, together with numerous other uranium minerals: lepersonnite-(Gd), becquerelite, curite, kasolite, oursinite, rutherfordine, schoepite, sklodowskite, soddyite, studtite, torbernite, and uranophane.

Crystal structure

Although originally though to be orthorhombic, bijvoetite-(Y) was later shown to be monoclinic. The structural formula of the mineral is [M3+83+(H2O)25(UO2)16O8(OH)8(CO3)16](H2O)14, where M = (Y,REE). The structure has 16 uranium sites, with uranium belonging to near-linear uranyl groups. The important features of the structure are:[1]

  • presence of uranyl pentagonal bipyramids (UPB), formed by coordination of (eight) uranyl groups by three oxide and two hydroxyl anions
  • presence of uranyl hexagonal bipyramids (UHB), formed by coordination of another eight uranyl groups by six oxide anions
  • presence of uranyl carbonate chain parallel to [100], of a novel type, built of edge-sharing dimers of UPB and UHB, and carbonate groups
  • presence of irregular M3+Φn polyhedra (Φ - unspecified ligand) linking the uranyl carbonate chain, thus forming a compound novel-type sheet parallel to (010)
  • location of 14 water molecules in the interlayer space (held by hydrogen bonding)
  • bonding of the remaining 25 water molecules to trivalent cations

References
  1. Li, Y., Burns, P. C., and Gault, R. A., 2000. A new rare-earth-element uranyl carbonate sheet in the structure of bijvoetite-(Y). The Canadian Mineralogist 38, 153-162.
  2. Deliens, M., and Piret, P., 1982. Bijvoetite et lepersonnite, carbonates hydrates d'uranyle et des terres rares de Shinkolobwe, Zaïre. Canadian Mineralogist 20, 231-238
  3. "Bijvoetite-(Y) - Handbook of Mineralogy" (PDF). Handbookofmineralogy.org. Retrieved 2016-03-12.
  4. "Bijvoetite-(Y): Bijvoetite-(Y) mineral information and data". Mindat.org. Retrieved 2016-03-04.
  5. "Kamotoite-(Y): Kamotoite-(Y) mineral information and data". Mindat.org. Retrieved 2016-03-10.
  6. "Sejkoraite-(Y): Sejkoraite-(Y) mineral information and data". Mindat.org. Retrieved 2016-03-10.
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